1. Field of the Invention
The present invention relates generally to the field of digital communications. More particularly, the invention relates to a communications interface circuit which detects if it is connected to a network or another communications system and which facilitates the reduction of overall power consumption when the interface circuit detects that it is not thus connected.
2. Related Art
Various communication interface standards are known for establishing connections between computer systems and peripheral devices. One example of such an interface is the RS-232 serial communication interface standard which is used in many applications, including IBM compatible personal computers. Conventionally, the circuitry used to provide a computer system with RS-232 communication interface capability remains active and powered even when not connected to a device. In the past, when computer systems were generally powered via a standard electrical outlet, this constant utilization of power did not present a problem because of the virtually inexhaustible supply of power available.
However, with the recent popularity of portable laptop and palmtop computers, which generally draw power from a rechargeable battery, this unnecessary power consumption has become problematic. Without a check on the status of its connection to other systems, the unused interface circuitry continues to drain power from the rechargeable battery, thereby reducing the amount of time the portable computer system may be used remotely.
To reduce this unnecessary power consumption, and thereby extend the time the rechargeable battery remains charged, it is desirable to provide a communication interface circuit which detects when it is not coupled to another communications system, and which provides a signal in response so that the application of power to certain portions of the interface circuit can be suspended.